Conical loudspeakers have been known for some time in the prior art, and therefore do not require detailed discussion with regard to their structure and operation. For better comprehension, however, it should be mentioned at this point that conical loudspeakers ordinarily consist of a magnet system, a loudspeaker frame, and a membrane onto which the moving coil is applied. The conical loudspeaker frame is conventionally made of either metal or plastic. The magnet system consists of an annular permanent magnet, and upper pole plate (made of metal and also annular), and a circular lower pole plate that is also made of metal. The two pole plates are joined to the annular surfaces of the permanent magnet. Also present is a circular pole core, one end of which is joined to the lower pole plate, and which is encased over its entire length, at a distance, by the inner contour of the upper pole plate and permanent magnet.
The base of the loudspeaker frame is joined to the surface facing away from the permanent magnet. In the prior art, this joint is effected as a rivet joint if the loudspeaker frame is made of metal. For this purpose, "rivet lugs" are formed on the surface of the upper pole plate facing away from the permanent magnet, and are guided through corresponding openings in the frame base. The region of the particular rivet lug that projects out from the frame base is expanded by riveting, and thereby clamps the frame base against the upper pole plate. In addition, the rivet lugs center the upper pole plate on the loudspeaker frame.
It is impossible, or possible only at the cost of considerable disadvantages, to transfer the aforementioned joint between loudspeaker frame and magnet system to loudspeaker frames that are made of plastic. Whereas the riveting procedure is designed to press the upper pole plate gently against the frame base, the forces required for that purpose acting on the rivet bumps and the frame base during the riveting process are so great that the frame base breaks.
To eliminate these problems --which are particularly common in large-scale series production of loudspeakers--the prior art indicates two possible solutions which guarantee that the loudspeaker magnet systems, which in some cases are heavy, can be secured to the frame base with sufficient security.
According to the first approach, the loudspeaker frame is adhesively bonded to the magnet system. Two-component adhesives are usually used for this purpose; in order to maintain production, they require large quantities of solvents and rinsing agents to keep the adhesive nozzle clear.
With the second approach, a "shaved rivet" joint is made to join the magnet system and loudspeaker frame. To do so, the rivet bumps are pressed into the corresponding openings in the frame base. This type of joint, however, demands the use of high-quality plastics for the loudspeaker frame, so as to prevent cold forming of the plastic with accompanying loosening of the joint. Plastics that exhibit the material characteristics suitable for this purpose are polycarbonates or glass fiber-reinforced polycarbonates. Aside from the fact that these polycarbonates are very expensive in comparison to other plastics, they are also not entirely without hazard from an environmental point of view, since this material is more or less non-degradable. If polycarbonate is used as a material for the loudspeaker frame, and if the loudspeaker frame later needs to be separated from the magnet system again, residues of the frame base will, as with the previously discussed solution using adhesive bonding, inevitably remain behind on the magnet system unless complex separation processes are implemented. As a result, the magnet systems are no longer available for re-use after they have been separated from the loudspeaker frame. The portions of the frame remaining behind on the magnet system are likewise permanently excluded from potential recycling processes for frame materials.